1. Field of the Invention
This invention relates generally to a hydraulic system in which a hydraulic booster and another hydraulically operating device receives pressurized fluid from a common hydraulic pump, and more particularly to a hydraulic booster which operates quickly in response to operations by a driver while preventing the pumping pulsations from being perceived by the driver.
2. Description of the Prior Art
A hydraulic booster of this class is disclosed, for example, in U.S. Pat. No. 4,075,848, patented Feb. 28, 1978 in which the pressurized fluid from a hydraulic pump is apportioned to two circuits by a distributor valve, one circuit leading to a reservoir through a pressure chamber of a hydraulic booster and a normally open valve operated by a driver and the other leading to the reservoir through another hydraulically operating device such as a power steering unit. The system further includes a change-over valve which is associated with the input piston of a normally open valve and adapted to elevate the discharge pressure of the oil pump to a level considerably higher than that of the aforementioned pressure chamber at the time of boosting operation by restricting the flow of fluid from the distributor valve to the pressure chamber, and a normally closed valve which is opened to admit the discharge pressure of the oil pump into the pressure chamber after the normally open valve is completely closed.